1. Field of the Invention
The present invention relates to a contact probe to electrically test semiconductor substrates, liquid crystal displays and the like, and a method of fabricating such a contact probe.
2. Description of the Background Art
Testing of circuitry formed on semiconductor substrates, liquid crystal displays and the like is generally performed using a testing device with a plurality of contact probes. The conventional structure of each of such contact probes is as described in, for example, Japanese Utility Model Laying-Open Nos. 6-22964 and 6-22965. A structure thereof is shown in FIG. 18. Referring to FIG. 18, a contact probe 100 has a barrel 103 placed in a socket 104. A spring 102 employing a coil spring is arranged in barrel 103. A plunger 101 to make contact with a circuit that is to be tested is urged by spring 102 in a direction protruding from the end of barrel 103.
According to this structure, plunger 101, spring 102, barrel 103 and socket 104 are individual components. In assembly thereof, plunger 101 and spring 102 are inserted into barrel 103 so that spring 102 urges plunger 101 outwards, followed by inserting this barrel 103 into socket 104.
In accordance with the higher density and microminiaturization of the circuitry that is the subject of testing, more contact probes are now being mounted at higher density per one testing device. As a result, a plurality of contact probes must be arranged at small pitches of not more than 0.1 mm.
The conventional contact probe 100 as described with reference to FIG. 18 had to be assembled from individual components such as plunger 101, spring 102, barrel 103 and socket 104. Therefore, in accordance with the fine geometry of the contact probe, the assembly process has become more difficult since respective components are correspondingly reduced in size. Since each component is conventionally fabricated by machining, the size of each component is also reduced in accordance with the microminiaturization of contact probes. The machining process of each component has become more difficult. Particularly when components formed by machining are to be arranged at the pitch of not more than 0.1 mm, the thickness of each component will become the bottleneck in the arrangement.
In the case where many contact probes are to be mounted in one testing device, the cost for component machine work will become higher in proportion to the increase of the number of contact probes since each contact probe component was conventionally formed by machining. The demand in the field of art could not be satisfied sufficiently.
In accordance with the increase in speed of the circuit operation and reduction in the pitch, crosstalk noise between contact probes has become noticeable. Such noise will degrade the detection sensitivity.
In view of the foregoing, an object of the present invention is to provide an ultra fine contact probe to correspond to reduction in the pitch, and a method of fabricating such a contact probe.
Another object of the present invention is to provide a contact probe that has the shielding function to prevent crosstalk noise even when of an ultra fine structure.
According to an aspect of the present invention, a contact probe includes a plunger unit to form contact with a circuit to be tested, a spring unit supporting the plunger unit at one end, and a lead wire connection unit electrically connecting the other end of the spring unit with a lead wire. The plunger unit, the spring unit and the lead wire connection unit are formed integrally. This structure eliminates the need to form each component and assembly thereof. Reduction in the size of the contact probe and increase in the number of contact probes can be accommodated more easily.
In the invention of the present aspect, the plunger unit, the spring unit and the lead wire connection unit are formed integrally so as to have a three dimensional configuration with uniform thickness with respect to a predetermined plane configuration in a thickness direction perpendicular to the predetermined plane configuration.
By employing the above-described structure, a contact probe, even of an ultra fine structure, can easily be fabricated as an integral object according to a fabrication method of a combination of lithography and plating using a predetermined mask.
In the invention of the present aspect, the contact probe preferably includes a guide unit arranged parallel to the spring unit to maintain the spring unit at a constant posture. The plunger unit, spring unit, lead wire connection unit and guide unit are formed integrally. By this structure, the step of assembling the guide unit can be eliminated even if a guide unit is required depending upon the usage status of the contact probe.
In the invention of the present aspect, the plunger unit, spring unit, lead wire connection unit and guide unit are preferably formed integrally so as to form a three dimensional configuration with uniform thickness with respect to a predetermined plane configuration in a thickness direction perpendicular to said predetermined plane configuration.
By the above structure, a contact probe including a guide unit, even of an ultra fine structure, can be easily fabricated as an integral object according to a fabrication method of a combination of lithography and plating using a predetermined mask.
In the invention of the present aspect, the contact probe preferably includes a cylindrical member including a conductor having the inner wall covered with an insulator. The cylindrical member surrounds the outer side of the spring unit. The plunger unit protrudes from the cylindrical member. This structure allows the cylindrical member to function as a guide unit. Since the cylindrical member includes a conductor, the spring unit is shielded by the cylindrical member to prevent crosstalk noise.
In the invention of the present aspect, the lead wire connection unit and the cylindrical member are fixed with respect to each other. By this structure, displacement of the cylindrical member during usage can be prevented.
Preferably, the spring unit has a configuration in which a leaf spring of a unitary configuration is repeated several times and connected. By this structure, a mask of only a simple pattern is required. A spring unit having a uniform spring constant at all sites can be provided.
Preferably, the spring unit includes a stopper for each of said unitary configuration. The stopper is arranged so as to abut against the leaf spring of the above-described unitary configuration to prevent further elastic deformation when the elastic deformation in the longitudinal direction of the spring unit exceeds a predetermined value. This structure prevents the spring from exceeding the elasticity limit to achieve plastic deformation and become disabled.
Preferably, the plunger unit includes a top portion and inclination portions sandwiching the top portion. The inclination portions are angled at not more than 90xc2x0 with respect to each other. The radius of curvature of the transverse section of the top portion is not more than 5 xcexcm. By this structure, the insulating film such as a natural oxide film formed at the surface of the circuit to be tested can easily be broken through to ensure electrical contact.
Preferably, a portion or all of the surface of the plunger unit including the top portion is covered with a material of low volume resistivity that is lower than the volume resistivity of the material inside the plunger unit. By this structure, the electrical contact resistance when the plunger unit is brought into contact with the circuit to be tested can be reduced to ensure stable electrical contact.
According to another aspect of the present invention, a method of fabricating a contact probe is provided. The contact probe includes a plunger unit to form contact with a circuit to be tested, a spring unit supporting the plunger unit at one end, and a lead wire connection unit electrically connecting the other end of the spring unit with the lead wire. The plunger unit, the spring unit and the lead wire connection unit are formed integrally so as to have a three dimensional configuration with uniform thickness with respect to a predetermined plane configuration in a thickness direction perpendicular to the predetermined plane configuration. The contact probe fabrication method includes a resist formation step of coating a resist on a substrate having conductivity, an exposure step of exposing the resist using an integral mask, a first resist removal step of removing the portion of the resist exposed at the exposure step, a forming step of filling the portion of the resist removed at the first resist removal step with metal, a second resist removal method of removing the remaining portion of the resist, and a substrate removal step of removing the substrate. As the integral mask, a mask of a configuration having the contact probe projected in the thickness direction is employed.
By the above-described fabrication method, a contact probe having the plunger unit, spring unit and lead wire connection unit formed integrally can be easily fabricated. Reduction in the size and complexity of the contact probe can be accommodated. Furthermore, the assembly process is unnecessary.
Preferably, the contact probe further includes a guide unit arranged parallel to the spring unit to maintain the spring unit at a constant posture.
By the fabrication method, a contact probe having the plunger unit, spring unit, lead wire connection unit and guide unit formed integrally can be easily fabricated. Also, reduction in the size and complexity of the contact probe can be accommodated. Furthermore, the assembly process is unnecessary.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.